This invention relates to a process for the preparation of a mixture of methyl- or ethyl-substituted anilines.
Methyl- and ethyl-substituted anilines are useful in a variety of applications such as in the preparation of dyes, herbicides, insecticides, plant growth agents and antiknock agents for gasoline engines. The anilines are generally prepared by nitration of the appropriate methyl benzene followed by reduction of the resulting nitro compound. This process depends upon the availability of the appropriate nitro compound which in some instances is unavailable or available only in limited quantities. For example, m-toluidine is important as an intermediate in dyes and agricultural chemicals. However, in the foregoing nitration-reduction process, only 4% of the toluidines produced are m-toluidine.
European patent application No. 92,103 discloses a process for preparing o-toluidine and/or m-toluidine and/or p-toluidine in two steps: (a) treatment of a toluidine isomer mixture or any undesired toluidine isomer with an isomerization catalyst from the series of the synthetic zeolites of the pentasil type, (b) isolation of the desired or one of the desired isomers from the mixture of isomers formed in step (a) through selective adsorption on a medium or large pore zeolite and subsequent desorption.
U.S. Pat. No. 3,868,420 discloses a process for producing phenylamines alkylated in the ortho and/or para positions by alkyl groups of 1 to 4 carbon atoms and unsubstituted on the amino group which comprises reacting a suitable phenylamine with an alkanol of 1 to 4 carbon atoms in the vapor phase at a temperature of from 350.degree. to 450.degree. C. in the presence of an aluminum oxide catalyst or an aluminum oxide/molybdenum oxide mixed catalyst.
U.S. Pat. No. 3,931,298 discloses a process for converting hydroxy-substituted aromatic compounds to the corresponding amine by reacting the aromatic hydroxy compound with ammonia in the presence of a catalytic amount of a cyclohexane and in contact with a hydrogen-transfer catalyst. U.S. Pat. No. 3,960,962 discloses a similar process wherein the catalyst comprises metallic palladium bonded to a phosphinated polystyrene resin.
U.S. Pat. No. 4,188,341 discloses a process for making 2,6-dimethylaniline or an N-substituted 2,6-dimethylaniline comprising reacting an enamine of a specified formula at a temperature of between -30.degree. C. and 150.degree. C. with acrolein in the presence of an inert aprotic solvent and heating the resulting reaction product to a temperature of between 100.degree. and 400.degree. C. in the presence of a hydrogen-transfer catalyst and an amine of the formula RNH.sub.2 wherein R is --H or a specified lower alkyl.
Japanese Kokai No. 53-28128 discloses a process for para-methylation of anilines comprising reacting an aniline having para-hydrogens with methanol in the presence of an alkali metal synthetic zeolite catalyst, particularly NaY zeolite. Preparation of 2,4-dimethylaniline from o-toluene and the preparation of p-toluidine from aniline are specifically disclosed.
Inoue et al., Seikyu Gakkaishi, 15, 372 (1972) studied the methylation of aromatic compounds with methanol in vapor or liquid phase on various catalysts and specifically report the orthomethylation of aniline with methanol using 10% MgO/Al.sub.2 O.sub.3 catalyst to produce o-toluidine.
Japanese patent publication No. 28129/1978 discloses demethylation of polymethylanilines, which contain at least more than two methyl groups, in the presence of a catalyst composition of the formula A.sub.a B.sub.b C.sub.c O.sub.d wherein A is titanium; B represents more than one kind of element selected from zinc, zirconium and magnesium; C represents more than one kind of element, selected from cobalt, nickel, copper, molybdenum, tungsten, barium, vanadium, chromium, manganese, tin, iron, calcium; O is oxygen; a is 1, b is 0.05 to about 20, and c is 0 to 1.0.
Japanese patent publication No. 1974-[Showa-49], 29,178 discloses a process for the synthesis of toluidines rich in m-toluidine by dealkylation of xylidines having a methyl group in a meta position in the presence of a dealkylation catalyst such as silica-alumina, alumina, silica, silica-magnesia and magnesia. Matsumoto et al., Chemistry Letters, pages 435 to 438 (1978) disclose a process for preparing m-toluidine by hydrocracking 2,3-xylidine over metal oxide-supported nickel catalysts. The authors disclose that the selectivity of m-toluidine is influenced by side reactions, such as isomerization, and that the extent of isomerization can be related to the acidic character of the metal oxide carriers.